The overall goal of the research proposed in this application is to identify the cellular and molecular triggers that initiate fatal cardiac arrhythmias and to determine novel gene-targeted therapeutic strategies to treat them. Our central hypothesis is that one step in this process is perturbation of membrane electrical activity caused by alteration in the biophysical and regulatory properties of surface membrane ion channel proteins and/or in key signaling molecules (in collaboration with Project 1) by diseased- linked mutations. This changes in channel activity may alter the configuration may alter the configuration 4) and, in turn, triggers arrhythmic. Altered ion channel properties may also confer unique pharmacological properties upon the encoded ion channels and/or signaling molecules linked to the long QT syndrome (LQTS) and Brudaga's syndrome (BrS) as paradigms to test these hypotheses. There are three aims of this project. Aim 1 is to test the hypothesis that there is heterogeneity in biophysical properties of mutant ion channels that are causally related to cellular and disease phenotypes. Aim 2 is to test the hypothesis that heterogeneity in disease-linked channel properties confers beta-receptor/channel coupling either by mutations (polymorphisms) in signaling or in ion channel molecules disrupts channel regulation in a manner that increases the risk of an arrhythmic event. Experiments that are proposed will combine patch clamp measurement of recombinant channel activity transiently expressed in mammalian cells. Theoretical testing of our predictions will be carried out using computer-based simulations of cardiac action potentials that incorporate our patch clamp data. In addition, systemic measurements (ECG) in genetically-altered animal models will be used to test the relationship between changes in ion channel properties and the genesis of arrhythmic activity in the heart. We hypothesize that information gained from these cellular and molecular experiments can be translated directly to improved therapeutic intervention in man. Thus this work has the potential to determine a mechanistic basis for Sudden Cardiac Death (SCD) at the molecular level, and to develop therapeutic strategies in man based on specific properties for mutant gene products.